1. Field of the Invention
This invention relates to pharmaceutical aerosol formulations. In another aspect this invention relates to pharmaceutical solution aerosol formulations wherein the propellant comprises a hydrofluoroalkane propellant such as 1,1,1,2-tetrafluoroethane or 1,1,1,2,3,3,3-heptafluoropropane. In another aspect this invention relates to pharmaceutical aerosol formulations containing butixocort propionate.
2. Description of the Related Art
Butixocort propionate (11-beta-hydroxypregn-4-ene-3,20-dione-21-thiopropionate-17-butyrate is an antiinflammatory steroid disclosed in U.S. Pat. No. 4,933,331 (Aubard et at.).
Current propellant-based pharmaceutical aerosol formulations use a mixture of liquid chlorofluorocarbons as the propellant. Fluorotrichloromethane, dichlorodifluoromethane and dichlorotetrafluoroethane are the most commonly used propellants in aerosol formulations for administration by inhalation. Such chlorofluorocarbons (CFCs), however, have been implicated in the destruction of the ozone layer and their production is being phased out. Hydrofluorocarbon 134a HFC 134a, 1,1,1,2-tetrafluoroethane) and hydrofluorocarbon 227 (HFC 227, 1,1,1,2,3,3,3-heptafluoropropane) are said to be less harmful to the ozone than many chlorofluorocarbon propellants.
Pharmaceutical aerosol formulations for inhalation most commonly contain a drug in the form of solid particles of respirable size suspended in the propellant system. Formulations involving dissolved drug are also known but have generally been less preferred because of the tendency of compounds (including drug substances) to be much more chemically reactive (and therefore unstable) in solution than in the solid state.